Electric switch



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Patented Apr. 9, 1929.

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GEORG STERN, OF OBERSCHDNEWEDE, NEAR BEELN, GERMANY, ASSIGNOR TO GEN- @RAL EL""C'i- MPJNY, .EL COR'RATION 0F NEVLT YORK.

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Application filed March 16, 1928, Serial No. 262,281?, and in Germany March 1927.

My invention relates to electric switches of the liquid break explosion chamber type. Switches ot this type are commonly constructed with metal ez-ialosion chambers, usually steel, in which is mounted the fixed contact and in which initiallyoccurs any are that isv drawn by the withdrawal of the movable contactA To prevent the arc from striking to the chamber which is in electrical connection with the fixed contact the chamber usually has been covered with a fibrous insulating material in the orm of cylinders, plates, bushings, etc. ln certain cases l have tound'that such insulation is not suiiicient to prevent an arc from -torming between the movable lcontact and the metal of the chamber, particularly when a breaking by the arc first drawn has been immediately followed by an excess volt-age. The movable contact being still relatively close to the chamber, an arc has become established between the moving contact and the chamber through the joints in the insulain' object ot' my invention, therefore, is to provide an improved switch of the type described which shall avoid the objectionable action mentionedk above.

My invention will be better understood from the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims. l

Referring to the single ligure ot the drawing, which is a sectional view illustrating an embodiment of my invention, the switch comprises the fixed contact l shown in the form of a socket and the movable contact 2 shown as a rod adapted when raised to closed circuit position to engage in the socket oit contact l. he iii/:ed contact l is enclosed by the explosion chamber 8 comprising the top plate l and the cup-like member 5, members l and 5 being shown secured together by screw threads. Although not shown in detail on the drawing it will be understood that means are provided or making a circuit connection with the xed contact l and -for securing this contact to the top plate 4l which means are well known to those iamiliar with electrical switches of this type. The member 5 thus is in electrical connection with the contact l. In the bottom of member is an opening through which the contact rod 2 is moved to engage the iiXed contact and through which it is withdrawn in the opening movement of the switch. In accordance with myinvention, I provide the explosion chamber with the covering 6 of insulation which seamless throughout its extent. It covers all those portions of member 5 to which there is any danger of an arc striking from the contact rod 2. As shown in the drawing, the insulation extends in a continuous layer over both the inside and the outside surfaces or member 5 and through the opening in the bottom thereof. For thus insulating the explosion chamber I employ preferably an insulating material which may be applied in the plastic form and which becomes rigid. l have ound an insulating material comprising an asbestos composition with a suitable binder such as a synthetic or natural resin and known to the trade as Tenazit to be well suited for this purpose, the material being molded to the member o while subjected to heat. lf it is found that the insulating material under certain conditions requires protection from the heat of the arc it is obvious that a covere ing of suitable material may be applied thereto. The seamless insulating material 6 need be used only on those portions of the explosion chamber to which 'there is danger of an arc striking, other parts of the switch which require insulation being insulated in any well known and suitable manner.

What I claim as new and desire to secure by `Letters Patent of the United States, is

l. ln an electric switch of the liquid break type, a ixed contact, a cooperating movable contact rod, and an explosion chamber enclosing .the fixed contact and having an opening tor receiving the contact rod, said chamber having insulating material thereon extending ina seamless covering over the exterior through the opening and over the interior.

2. In an electric switch of the liquid break type, an explosion chamber having an opening therein, a fixed contact within and electrically connected with the chamber, a cooperating contact rod adapted to be with-l drawn from the fixed contact through said opening, and means for preventing an arc becoming established between the contact rod and the chamber comprising a seamless covering ot insulation applied to those parts oi the chamber to which the arc is liable to strike.

3. An electric switch of the liquid break type comprising :i iixed Contact, av cooperating` movable Contact, and an explosion chainbei enclosing the fixed Contact and having 1 fin opening therein foi* receiving` the inovabe Contact, said explosion Chamber having' a seamless covering of insulating material Comprising asbestos and resin extending Vthrough the opening,` and ovei adjacent inner and Outer portions of the chamber.

In Witness whereof, I have hereunto Set my hand hie 24th day o February, 1928.

GEORG STERN. 

